The Shockwave Theory

Theory Attempting to Explain Destruction Outracing Rubble

According to the shockwave theory, the "gigantic impact forces"
caused by the tower's top falling into the intact structure below
the impact zone sends a shockwave through that structure,
breaking it up even before the falling top reaches it.

The most conspicuous exposition of this theory was
an article entitled
World Trade Center - Some Engineering Aspects
published on the website of
the University of Sydney's Department of Civil Engineering website.
Versions of this article are widely copied on the web,
and it is excerpted in
Muslims Suspend Laws of Physics!
first published on October 21, 2001,
suggesting that the Sydney article was published soon after the attack.
A version of the article archived on
the Web archive
contains the following excerpt:

This photograph shows the south tower just as it is collapsing.
It is evident that the building is falling over to the left.
The North Tower collapsed directly downwards, on top of itself.
The same mechanism of failure, the combination of impact and
subsequent fire damage, is the likely cause of failure of both towers.
However, it is possible that a storey on only one side of the South Tower
initially collapsed, resulting in the "skewed" failure of the entire tower.

The gigantic impact
forces caused by the huge mass of the falling structure landing on the
floors below travelled down the columns like a shockwave faster than the
entire structure fell. The clouds of debris coming from the tower,
several storeys below the huge falling mass, probably result from the
sudden and almost explosive failure of each floor, caused by the
"shockwave".

In later versions of the article, the passage has been changed
to remove the shockwave theory,
while other copies retain the shockwave theory.
2Â

This photograph shows the south tower just as it is collapsing.
It is evident that the building is falling over to the left.
The North Tower collapsed directly downwards, on top of itself.
The same mechanism of failure, the combination of impact and
subsequent fire damage, is the likely cause of failure of both towers.
However, it is possible that a storey on only one side of the South Tower
initially collapsed, resulting in the "skewed" failure of the entire tower.

While the ways the two towers fell were slightly different,
the basic cause is similar for both - a large number of columns
were destroyed on impact, and the remaining structure was gradually
weakened by the heat of the fire. Not much significance should be
taken from the fact that one tower fell in 45 minutes and the other
in 90 minutes.

The gigantic dynamic impact forces caused by the huge mass of
the falling structure landing on the floors below is very much
greater than the static load they were designed to resist.